1. Field of the Invention
This invention relates to an implantable medical device, such as an expandable, intraluminal prosthesis commonly known as a stent. More particularly, this invention relates to a stent having depots formed in its cylindrical body, as well as a method of depositing agents, such as therapeutic agents, in the depots.
2. Description of the State of the Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. An implantable medical device is introduced into the cardiovascular system of a patient via the brachial or femoral artery. The device is advanced through the coronary vasculature until the device is positioned across the occlusive lesion.
A problem associated with the procedure includes formation of intimal flaps or torn arterial linings which can collapse and occlude the conduit after the device is implanted. Moreover, thrombosis and restenosis of the artery may develop over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. To reduce the partial or total occlusion of the artery by the collapse of arterial lining and to reduce the chance of the development of thrombosis and restenosis, an intraluminal prosthesis, an example of which includes an expandable stent, is implanted in the lumen to maintain the vascular patency. Stents are scaffoldings, usually cylindrical or tubular in shape, functioning to physically hold open, and if desired, to expand the wall of the passageway. Typically stents are capable of being compressed for insertion through small cavities via small catheters, and then expanded to a larger diameter once at the desired location.
In treating the damaged vasculature tissue and to further fight against thrombosis and restenosis, there is a need for administrating therapeutic substances to the treatment site. For example, anticoagulants, antiplatelets and cytostatic agents are commonly used to prevent thrombosis of the coronary lumen, to inhibit development of restenosis, and to reduce post-angioplasty proliferation of the vascular tissue, respectively. To provide an efficacious concentration to the treated site, systemic administration of such medication often produces adverse or toxic side effects for the patient. Local delivery is a highly suitable method of treatment in that smaller levels of medication, as compared to systemic dosages, are concentrated at a specific site. Local delivery produces fewer side effects and achieves more effective results.
One commonly applied technique for the local delivery of the drugs is through the use of medicated stents. A proposed method involves the use of a polymeric carrier coated onto the body of the stent, as disclosed in U.S. Pat. No. 5,464,650 issued to Berg et al., U.S. Pat. No. 5,605,696 issued to Eury et al., U.S. Pat. No. 5,865,814 issued to Tuch, and U.S. Pat. No. 5,700,286 issued to Tartaglia et al. Obstacles often encountered with the use of a polymeric coating include difficulties in coating a complicated geometrical structure, poor adhesion of the polymeric coating to the surface of a stent, and biocompatibility of the polymer.
The art continues to develop more reliable ways to control the release profile of agents from a medical device or a coating. Such control can be important to obtain the desired effects or reduce any adverse effects that may otherwise occur from administration of the agents. In addition to providing a way to improve the bioactive, biobeneficial, and/or diagnostic results currently obtained from the administration of agents, control over the release rate of agents can assist in designing and maintaining the physical and mechanical properties of medical devices and coatings as well. Accordingly, control over the release of agents is an important design consideration and one of the next hallmarks in the development of stent technology.